Hypothesis

Shear-banding of branched wormlike solutions is a topic of active investigation which has not been fully elucidated. Here, we surmise that flow-induced microstructuring in the shear banding regime is associated with spatial concentration gradients.

Experiments

The experiments focus on the flow-induced behavior of a CTAB/NaSal wormlike micellar system. A unique approach based on a microfluidic-spitter geometry, combined with particle-image velocimetry and high-speed video microscopy, is used to separate the streams flowing out from the core and the near wall zones of the microchannel.

Findings

Here, we present the first direct experimental evidence of the correlation between phase separation and shear banding. By increasing the pressure-drop across a microcapillary, the onset of a grainy texture close to the wall, showing a flow-induced demixing effect, is observed. We use a splitter to measure effluent streams from the center and the near-wall zones in terms of viscosity, conductance and dry mass. We observe that phase-separation induced by the flow correlates with chemical concentration gradients. This confirms our hypothesis that shear-induced local de-mixing of the system is strongly related to chemical concentration gradients.

中文翻译：

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分支蠕虫状胶束溶液剪切带中的流致浓度梯度

假设

分支蠕虫解的剪切带是一个积极研究的话题，尚未得到充分阐明。在这里，我们推测剪切带中的流致微观结构与空间浓度梯度有关。

实验

实验着重于CTAB / NaSal蠕虫状胶束系统的流动诱导行为。一种基于微流控散射体几何形状的独特方法，结合了颗粒图像测速和高速视频显微镜技术，用于分离从微通道核心和近壁区域流出的流。

发现

在这里，我们提出相分离和剪切带之间相关性的第一个直接实验证据。通过增加微毛细管上的压降，可以观察到靠近壁的粒状纹理的出现，显示出流动引起的混合效果。我们使用分流器从粘度，电导率和干重方面测量从中心和近壁区域流出的物流。我们观察到，流动引起的相分离与化学浓度梯度相关。这证实了我们的假设，即剪切引起的系统局部去混合与化学浓度梯度密切相关。